Light cycle oil (hereinafter, referred to as “LCO”), which is a cracked light oil produced by a fluid catalytic cracking (hereinafter, referred to as “FCC”) apparatus, and the like contain many polycyclic aromatic components, and so far, light cycle oil has been used primarily as light oil/heavy oil fractions. In recent years, there has been a demand for a technology of efficiently producing monocyclic aromatic hydrocarbons having 6 to 8 carbon atoms (for example, benzene, toluene, and crude xylene (xylene containing a small amount of ethylbenzene or the like); hereinafter, these will be collectively referred to as “BTX”) having a high added value, which uses LCO and the like as a raw material, and can be utilized as high octane value gasoline base materials or petrochemical raw materials.
Regarding the method for producing BTX from a polycyclic aromatic component, for example, methods described below and the like are known.
(1) A method of subjecting a hydrocarbon containing a polycyclic aromatic component to hydrogenation-cracking in a single stage (Patent Documents 1 and 2).
(2) A method of hydrogenation-treating a hydrocarbon containing a polycyclic aromatic component in an earlier stage and then subjecting the product to hydrogenation-cracking in a later stage (Patent Documents 3 to 5).
(3) A method of directly converting a hydrocarbon containing a polycyclic aromatic component to BTX by using a zeolite catalyst (Patent Document 6).
(4) A method of converting a mixture of a hydrocarbon containing a polycyclic aromatic component and light hydrocarbons having 2 to 8 carbon atoms to BTX by using a zeolite catalyst (Patent Documents 7 and 8).
However, in the methods of (1) and (2), addition of molecular hydrogen at a high pressure is essential, and there is a problem that large hydrogen consumption is needed. Furthermore, under the conditions of the hydrogenation treatment, an LPG fraction and the like are produced to a large extent as side products, so that not only is energy required for separation thereof, but also the raw material efficiency is also decreased.
In the method of (3), conversion of the polycyclic aromatic component is not sufficiently achieved.
The method of (4) is a method of enhancing the thermal balance by combining a BTX production technology using light hydrocarbons as raw materials and a BTX production technology using a hydrocarbon containing a polycyclic aromatic component as a raw material, and this method does not always increase the yield of BTX from the polycyclic aromatic component.
Also available as a material containing a polycyclic aromatic component at a high concentration such as LCO, is a cracked heavy oil (thermally cracked heavy oil) that is obtained from an ethylene production apparatus. This cracked heavy oil is mostly used as a fuel for boilers in a Combinat. Regarding other utilization methods for the cracked heavy oil, it is known that an ethylene heavy end is treated in the presence of a solid acid catalyst in a hydrogen atmosphere, and thus a modified pitch from which the light-boiling fraction obtainable up to 500° C. is excluded, which is used as a raw material of carbon fibers, may be obtained (Patent Documents 9 and 10).
However, a method for producing, at a high yield, BTX by using such a thermally cracked heavy oil as a feedstock is not known.